<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>示例4,5</title>
</head>
<body>
    <script>
        const PI = 3.1415;
        // PI = 3; 报错

        const foo = {}
        foo.prop = 123;
        console.log(foo.prop)

        // foo = "jack"; 报错
    </script>
</body>
</html>